666 Waring ton ,— The Effect of Boric Acid and Borax on 
of the latter. But since a catalyst is essentially a substance not itself 
used up during the reaction upon which its presence depends, and since it is 
evident from the present work on the broad bean that the supply of boron 
must be continual in order to be effective, it would seem more probable that 
the action of the element is nutritive, and that it is in some way fixed by 
the plant and not in a state of circulation. 
It has been shown by a number of workers on the subject, that certain 
of the Leguminosae readily respond to the action of boron compounds, 
yet even in this comparatively small 'group of plants a great difference 
in the degree of response is shown. Boron is apparently essential to 
the broad bean, and, as far as preliminary evidence goes, probably also to 
several other plants, such as the runner bean, dwarf bean, and crimson 
clover; while peas, wild white clover, and winter vetch appear to be more or 
less independent of its presence, though even in these cases some slight 
beneficial effect is evident from the addition of small quantities of H :5 BO ;5 to 
the nutrient solution. 
The importance of the conditions under which the plant is growing on 
the reaction towards boron has been frequently seen during this investigation. 
For example, both the degree of toxicity of the same quantity of boric 
acid and the type of root developed in water culture by the untreated 
plants were found to vary with seasonal conditions, though the main results 
were independent of any such changes. High concentrations of boric acid 
were, for instance, considerably more injurious to broad beans grown in early 
spring or autumn than during the summer months, due probably to the fact 
that at such seasons growth was less vigorous and the plants less resistant 
to poisonous agents. 
The roots of the control plants both in broad beans and crimson clover 
were less abnormal in appearance when grown in the late autumn than 
when set up earlier in the year, the stunted growth being hardly noticeable 
in the former series or at most only after a long time. In this case also, 
the slow rate of growth probably accounted for the delay in the appearance 
of the effects of boron deficiency, the roots being able to develop normally 
for a considerable time. 
Whatever the function of boron, it is to some extent at least inde- 
« 
pendent of the food supply, whether limited or abundant, for in Brenchley’s 
(11 (rt)) work on the action of boric acid on peas and barley no renewal of 
the nutrient solution was made during the course of the experiment, yet the 
present results are in close agreement with this earlier work though the 
solutions were regularly renewed. 
Nitrogen plays such a leading part in the nutrition of all plants that 
the effect of boron on the quantity of nitrogen absorbed is of importance. 
Consideration of Tables X-XIII and Text-figs. 2, 4, 5, 6 shows that the 
application of excessive amounts of boric acid was correlated with an 
